The present invention relates to a novel process for preparing 3,3'- or 3,4'-diamino benzophenone.
3,3'- or 3,4'-diamino benzophenone is useful as monomers for heat-resistant polymers, agricultural or medical chemicals, intermediates for dyestuffs and the like. Particularly, they are important as raw materials for heat-resistant polyamide or polyimide resins.
In a conventional known process, 3,3'-diamino benzophenone is prepared by the reduction of 3,3'-dinitro benzophenone which has been prepared by the nitration of benzophenone. However, in the nitration reaction of benzophenone to 3,3'-dinitro benzophenone, there are required repeated refining operations by means of recrystallization for separating 3,3'-dinitro benzophenone from the reaction product containing impurities such as the isomers of the dinitro benzophenone (E. Barnatt et al., J. Chem. Soc., 125, 767 (1924)). Thus, the process is disadvantageous in that it produces only an extremely low yield of 3,3'-dinitro benzophenone and requires complicated operations for recovering the voluminous solvents used in the refining steps and for treating residuals, making the process uneconomical. The process has a further drawback in that the reduction of 3,3'-dinitro benzophenone to 3,3'-diamino benzophenone must be carried out using an excess amount of stannous chloride dissolved in a large amount of concentrated hydrochloric acid (L. H. Klemm et al., Org. Chem. 23, 351 (1958)), requiring the use of the costly stannous compound and the treatment of the spent metal and the spent acid. The process is therefore unsuitable for producing 3,3'-diamino benzophenone on a commercial scale, from the standpoint of both economy and environmental protection.
It has been conventionally known to prepare 3,4'-diamino benzophenone by the reduction of 3,4'-dinitro benzophenone. For preparing 3,4'-dinitro benzophenone, there have been known such processes as the process where 3,4'-dinitro diphenyl methane, which has been produced by the reaction of 4-nitro benzylalcohol and nitrobenzene, is oxidized by chromic acid (P. J. Montagne et al., Ber., 49, 2293-2294 (1916)), the process where diphenyl acetate is nitrated by fuming nitric acid to produce 3,4'-dinitro diphenyl acetate which is then oxidized by chromic acid (I. M. Hunsberger et al., J. Am. Chem. Soc., 71, 2635-2639 (1949)), and the process where 4-nitro benzophenone is nitrated (Vernon. L. Bell et al., J. Of Polymer Chem., 14, 2277 (1976)). However, these processes involve complicated reactions. They are also disadvantageous in that they require the repetition of refining operations by means of recrystallation for removing large amounts of by-products such as isomers, and further treatments of spent acids and/or metals, making the processes uneconomical. Thus, the 3,4'-dinitro benzophenones obtained by such processes cannot provide the raw materials for commercially producing 3,4'-diamino benzophenone.
It has been known to prepare 3,3'-dinitro-4,4'-dichloro benzophenone, one of the benzophenone derivatives to be used as starting material in the present invention, by the nitration of 4,4'-dichloro benzophenone. For example, it is known to nitrate 4,4'-dichloro benzophenone by nitric acid or sodium nitrate and sulfuric acid (E. R. Kofanav et al., J. Org. Chem. USSR, 15, 98-100 (1979)). However, such process has several drawbacks. For example, there is used a large amount of the mixed acid which must be subjected to a certain treatment after the completion of the reaction. Further, it is not easy to isolate the desired compound in a high purity from the reaction product, since the compound tends to take granular forms so as to bear the raw material and the acids therein. It is not easy to refine such compound after the completion of the reaction. It may be proposed to obtain the desired compound in a high purity by isolating said compound by means of filtering immediately after the crystallization from the mixed acid. However, such procedure is troublesome and impractical for commercial production of the desired compound. The prior art process has a further disadvantage from the standpoint of operational easiness and economy in that, as the nitration reaction is exothermal, the reaction must be carried out by adding the raw material stepwise in small doses to the reactor and/or cooling the reactor efficiently.
It has been therefore highly desired to develop a process for commercially producing 3,3'-dinitro-4,4'-dichloro benzophenone by the nitration of 4,4'-dichloro benzophenone in which the reaction heat can be controlled in an easy manner, there is used minimal amount of the mixed acid, the treatments after the reaction can be easily made, and further there can be obtained crystalline 3,3'-dinitro-4,4'-dichloro benzophenone in a high yield and purity.